Let There be Light!
Back in the '60s phones were hardwired to the wall. TVs were mostly black and white. And curing UV (ultraviolet) inks required mercury-vapor lamps with shutters and fans to control the light and temperature. Today, your phone is in your pocket and your color TV takes up a lot of wall space. So why are many package printers and converters still curing UV inks using technology that was state-of-the-art when the Beatles topped the charts?
The benefits of UV inks that were attractive in the '60s—high-gloss effects, resistance to chemicals, rub-off and scratching, and the range of substrates that can be used—are still compelling today. And although modern UV curing technology has stepped up to deliver those capabilities, most presses using UV inks still use essentially the same kind of mercury lamp systems as when the Mustang was a Detroit best-seller—and still face the same challenges. Mercury vapor lamps (which actually date back to about 1880) create the right frequency of UV light to cure the inks, but are burdened with fans, shutters, and the need for regular bulb replacement. In addition, warm-up and cool-down periods affect productivity, and high power consumption and hazardous waste disposal challenges add to the cost of every package produced. While the old technology could continue to be refined, it lacks the future-proof qualities printers and converters need when investing in new equipment.
The 21st century alternative is the LED, a tiny lamp that emits ultraviolet light (along with some visible blue or violet light). Unlike most conventional light sources, LEDs emit light in a narrow range of frequencies in the 385 to 395 nanometer range. Because most of the electrical power that goes into an ultraviolet LED is converted into those specific frequencies of light, less power is needed to achieve the same cure of ink on a substrate. On a press, the LEDs are arranged in compact arrays that span the width of a printed web and quickly cure UV inks as part of the printing and production process. The arrays use less power, have very long life spans, and present no environmental hazards in either the workplace or at disposal.
While such advantages would seem to make using LED curing a no-brainer, mercury vapor proponents have been quick to create a storm of fear, uncertainty and doubt (FUD), spreading myths of high costs, energy consumption concerns, and low availability of both LEDs and inks.
"Nothing could be further from the truth," affirms Greg Palm, EVP and director of business development at Mark Andy. " In fact, UV LED will totally eradicate all other types of heat curing within the next five years." And his comes from a man whose company sells both mercury and LED curing systems.
Myth #1: Price—One of the most recurrent myths is that the benefits of LED curing come at a significant price premium. And that seems true if you look only at the initial purchase price of the equipment. Dig a bit deeper and you find the cost difference disappears in a few months because LED systems are more efficient to own and operate. "When all the components are included the systems are actually fairly comparable in price, and the payback in operating costs for running LEDs can easily be less than a year," says Palm.
For example, an 8-color, 13-inch flexo press is about $110,000 with a traditional mercury system, while the same size LED system runs around $178,000. But for substrates that would be sensitive to the heat of mercury lamps, the basic system requires chiller rollers which raise the price to $166,000. Because the LED lamps are able to run film without web chilling, the premium for an LED system in this example is less than 10 percent.
Myth #2: Ink Selection—Another myth is that the range of UV ink is too limited and too expensive. "Inks have been an issue," admits Palm. "but that's not the case any more." In fact, major ink suppliers including Flint, Nazdar, Paragon, and Seigwerk offer UV curable inks and coatings, including metallic inks and shrink whites. And while pricing of inks is based on a customer's volume, prices of $16–20 per pound are common.
Myth #3: Substrates—Substrate limitations? Not so much. UV LED can work with self-adhesive labels (including coated and uncoated papers, BOPP, PE, PLA and synthetic films), shrink sleeves (PET-G, PVC, OPS), carton board, unsupported films, and laminations. LEDs also work with heat-sensitive and thin substrates, and both rigid and flexible materials. Equally important, the intensity of the UV light and the curing can be carefully controlled when neded, allowing for faster or deeper curing—something that is difficult to do with mercury lamps.
Myth #4: LED Life—The last myth is the cost of replacing a pricey LED array. But that's unusual given array life expectancies of 20,000 hours, or nearly 10 years of running constantly for 40 hours a week. Mercury bulbs by comparison have average lifetimes of about 500 hours and need to be routinely stocked replacement parts for converters running mercury UV curing systems.
To be fair, mercury UV curing remains a perfectly valid way to cure the full range of UV-curable inks and makes great sense on older systems and when thin or heat-sensitive substrates aren't required. But for most new installations and for converters looking to decrease operating costs and increase efficiency, the stark cool light of LEDs shows the way to tomorrow. pP